Storm water runoff collected from roof areas and paved areas were historically directed into municipal storm water drainage systems and released into a local body of water. However, regulatory changes and good practice now mandate that storm water runoff must be collected and directed to local soil where it can replenish groundwater supplies.
The traditional construction of storm water handling systems has been concrete tanks or infiltration trenches filled with large gravel or crushed stone with perforated pipes running therethrough. Such stone filled trench systems are non-economical and/or inefficient since the stone occupies a substantial volume, limiting the ability of the system to handle large surge volumes associated with heavy storms. Both the stone and the perforated pipe are also susceptible to clogging by particles or debris carried by water.
Molded plastic chamber structures were introduced to the market to take the place of concrete structures for handling storm water. U.S. Pat. No. 5,087,151 is an early patent in the field which discloses a drainage and leaching field system comprising vacuum-molded polyethylene chambers that are designed to be connected and locked together in an end-to-end fashion to provide a water handling system.
Storm water chambers typically have a corrugated arch-shaped cross-section and are relatively long with open bottoms for dispersing water to the ground. The chambers are typically buried within crushed stone aggregate or other water permeable granular medium that typically has 20-40 percent or more void space. The chambers serve as water reservoirs in a system that includes both the chambers and surrounding crushed stone. The crushed stone is located beneath, around, and above the chambers and acts in combination with the chambers to provide paths for water to percolate into the soil, and also provides a surrounding structure that bears the load of any overlying materials and vehicles. The chambers will usually be laid on a crushed stone bed side-by-side in parallel rows, then covered with additional crushed stone to create large drainage systems. End portions of the chambers may be connected to a catch basin, typically through a pipe network, in order to efficiently distribute high velocity storm water. Examples of such systems are illustrated in U.S. Pat. Nos. 7,226,241 and 8,425,148.
The use of molded plastic chamber structures has grown substantially since their initial introduction to the market, and have replaced the use of concrete structures in many applications. Molded plastic chamber structures provide a number of distinct advantages over traditional concrete tanks or stone-filled trench systems. For example, concrete tanks are extremely heavy requiring heavy construction equipment to put them in place. Stone-filled trench systems are expensive and inefficient since the stone occupies a substantial volume, limiting the ability of the system to handle large surge volumes of water associated with heavy storms.
More recently, manufacturers have begun to offer taller; bigger volume chambers having a larger storage capacity. A design consideration associated with larger size storm water chambers is that such structures may experience greater load stress than smaller chambers. A chamber should have a load bearing strength capable of bearing the load of the overlaying crushed stone and paving, and loads corresponding to use of construction equipment and vehicular traffic over the location of the buried chamber.
Various features have been incorporated into the structure of storm water chamber including the use of sub-corrugations into the corrugations so as to improve the strength of the plastic storm water chambers. While some of the proposed configurations have improved storm water chambers construction, there is still a need to improve the structural rigidity of multiple chambers that are connected to each other to form a field of chambers.
For example, one problem encountered by plastic storm water chambers during installation is that of the upright sides spreading apart relative to each other. It is typical for storm water chamber installations to occur during hot summer months when solar heating of the chambers is a significant problem, particularly in southern latitudes. As the plastic storm water chambers sit on the jobsite prior to installation, they absorb solar energy, which heats the plastic chambers, lowering the rigidity of the structures. When these heated plastic chambers are finally lowered into place in the bottom of a trench, the upstanding side walls can become relatively pliable causing them to spread apart from each other. This is especially a problem when crushed stone is dropped into the trench around and on top of the plastic chamber. The weight of the stone combined with the increased pliability of the plastic chamber can, in some instances, cause deformation or collapse of the chamber.
Therefore, there continues to be a need in the storm water management field for plastic storm water chambers that have structural elements to offset or negate the reduced rigidity of the upstanding side walls when rigidity is reduced due to, for example, solar heating.